1. Field of the Invention
The present invention relates to an image-bearing member protecting agent, a protective layer forming device which forms a protective layer on a surface of an image bearing member, and an image forming apparatus and a process cartridge, which includes the protective layer forming device, in an electrophotographic apparatus.
2. Description of the Related Art
Conventionally, in electrophotographic image formation, a latent electrostatic image is formed on an image bearing member made from a photoconductive material, and charged toner particles are attached to this latent electrostatic image so as to form a visible image. The visible image formed with the toner particles is transferred onto a transfer medium such as paper, a resin sheet, or the like, and then fixed on the transfer medium utilizing heat, pressure, solvent gas, or the like so as to form an output image.
Methods for the image formation are broadly classified, according to methods for charging toner particles to form a visible image, into so-called two-component developing methods in which frictional charging effected by stirring and mixing toner particles and carrier particles is utilized, and so-called one-component developing methods in which toner particles are charged without using carrier particles. Further, the one-component developing methods are classified into magnetic one-component developing methods and nonmagnetic one-component developing methods, according to whether or not magnetic force is utilized to keep toner particles on a developing roller serving as a developing member.
In image forming apparatuses, such as copiers, complex machines based upon the copiers, and the like for which high-speed processing capability and image reproducibility are required, the two-component developing methods have been employed in many cases due to demands for stable chargeability of toner particles, stable charge rising properties of the toner particles, long-term stability of image quality, and the like; whereas in compact printers, facsimiles, etc. for which space saving, cost reduction and the like are required, the one-component developing methods have been employed in many cases.
Also, nowadays in particular, colorization of output images is progressing, and demands for improvement of image quality and stabilization of image quality are increasing like never before. For the improvement of image quality, toners have been made smaller in average particle diameter, and particles of the toners have been made rounder in shape with their angular parts removed.
Generally, in an image forming apparatus which operates in accordance with any such electrophotographic image forming method, regardless of which developing method is employed, a drum-shaped or belt-shaped image bearing member (typified by a photoconductor) is uniformly charged while being rotated, a latent image pattern is formed on the image bearing member by laser light or the like, and the latent image pattern is visualized as a toner image by a developing unit and transferred onto a transfer medium.
After the toner image has been transferred onto the transfer medium, untransferred toner components remain on the image bearing member. If such residues are directly conveyed to a region for the charging step, it often hinders the image bearing member from being uniformly charged; accordingly, in general, the toner components, etc. remaining on the image bearing member are removed by a cleaning step by a cleaning unit after the transfer step, thereby bringing the surface of the image bearing member into a clean enough state, and then charging is carried out.
Thus, there are various types of physical stress and electrical stress in each step in image formation, which degrade the image bearing member, charging member and cleaning member. In attempts to solve this problem, a number of proposals for lubricants and methods of supplying lubricant components and forming films have been made thus far to reduce degradation of the image bearing member, charging member and cleaning member.
For example, Japanese Patent Application Publication (JP-B) No. 51-22380 proposes a method of forming a lubricant film on a photoconductor surface by supplying the photoconductor surface with a solid lubricant composed mainly of zinc stearate in order to lengthen the lifetimes of a photoconductor and a cleaning blade. This makes it possible to reduce abrasion of the photoconductor surface and thus lengthen the lifetime of the photoconductor.
However, it is understood that fatty acid metal salts such as zinc stearate lose their lubricating properties at an early stage due to electric discharge performed in the vicinity of the image bearing member in a charging step. Consequently, lubricating properties between the cleaning blade and the image bearing member are impaired, and toner particles pass through the cleaning blade (hereinafter also referred to as toner leakage), and thus defective images are formed.
In an attempt to solve this problem, Japanese Patent Application Laid-Open (JP-A) No. 2006-350240 proposes a method of applying an image-bearing member protecting agent which contains a fatty acid metal salt and boron nitride. Thus, the lubricating properties between a cleaning blade and an image bearing member can be maintained by means of a lubricating effect of the boron nitride even under the influence of electric discharge performed in the vicinity of the image bearing member in a charging step, and toner leakage can be prevented.
In JP-A No. 2007-145993, at least two types of higher fatty acid metal salts having different numbers of carbon atoms are used in order to improve the formability of an image-bearing member protecting agent with a large aspect ratio.
In JP-A No. 2006-350240, the boron nitride has the lubricating properties so as to prevent toner leakage. However, when the boron nitride is used for the image-bearing member protecting agent, its high lubricating properties make it difficult to remove the agent from the surface of the image bearing member, and thus the agent is attached onto the image bearing member as a film, which causes blurring of an image.
In the method of JP-A No. 2007-145993, although the formability of the image-bearing member protecting agent is improved, the lubricating property is reduced by the use of the different types of fatty acid metal salts, causing acceleration of the toner leakage and smearing on the charging member.